bob orr has been talking to his sources and has learned more. bob? >> reporter: well, scott, it's clear to us now that the gunman carefully planned his deadly attack for a very familiar target. as we reported, his mother was a kindergarten teacher at sandy hook elementary so he knew his way around the target zone. investigators believe the spree actually began earlier in the day at the home adam lanza shared with his mother. sources say she was killed there, then lanza drove to the school armed with at least three weapons. we're told he was carrying a sig sauer semiautomatic pistol and also a 9 millimeter glock handgun. he went directly to a very specific area of the school, he opened fire killing 20 kids in two nearby classrooms. we still don't know how many rounds he fired, but the handguns are capable of carrying extended magazines which can each hold up to 30 rounds of ammunition. now, also police found later a third gun, a bush master type .223 assault rifle in his mother's car which was parked outside the school. sources tell us tonight that al